Lipid Headgroup Discrimination by Antimicrobial Peptide LL-37: Insight into Mechanism of Action

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F. Neville, M. Cahuzac, O. Konovalov, Y. Ishitsuka, K.Y.C. Lee, I. Kuzmenko, G.M. Kale, D. Gidalevitz

Abstract:
Interaction of the human antimicrobial peptide LL-37 with lipid monolayers has been investigated by a range of complementary techniques including pressure-area isotherms, insertion assay, epifluorescence microscopy, and synchrotron x-ray scattering, to analyze its mechanism of action. Lipid monolayers were formed at the air-liquid interface to mimic the surface of the bacterial cell wall and the outer lea. et of erythrocyte cell membrane by using phosphatidylglycerol ( DPPG), phosphatidylcholine ( DPPC), and phosphatidylethanolamine ( DPPE) lipids. LL-37 is found to readily insert into DPPG monolayers, disrupting their structure and thus indicating bactericidal action. In contrast, DPPC and DPPE monolayers remained virtually unaffected by LL-37, demonstrating its nonhemolytic activity and lipid discrimination. Specular x-ray reflectivity data yielded considerable differences in layer thickness and electron-density pro. le after addition of the peptide to DPPG monolayers, but little change was seen after peptide injection when probing monolayers composed of DPPC and DPPE. Grazing incidence x-ray diffraction demonstrated significant peptide insertion and lateral packing order disruption of the DPPG monolayer by LL-37 insertion. Epifluorescence microscopy data support these findings.